[ScottR]

My local POCO, LIPA, woke me up this morning with the sound of a crane in my backyard. They also had a brand-new transformer with them.

I'd never seen them change one out before, so I thought you guys might be interested in some pics. I had a pretty good view from my bedroom window..

And that's when I had to leave for work.

This actually did not knock out power to my house. I was on that transformer until yesterday when they replaced the low voltage lines, and now apparently I'm being fed by a transformer that's upstream, to the right of these pics.

 

[micromind]

I've been the guy on the pole a few times. I like it a lot better if the top of the crane is above the top of the pole, the further the better. It's much easier to position the transformer if you have some line between the crane and the hook. Winching a transformer up a pole with no crane is quite a chore. That transformer likely weighs about 600 lbs.

That transformer is known as a 'single bushing'. The hot side of the primary (high voltage) side is the insulator on top. The other side is connected to the case, which is connected to the primary neutral. These transformers can be used only on a system where the primary neutral is grounded.

The other type is a 'two bushing'. It has two insulators on top, and can be used with a primary hot and a grounded neutral, or two primary hots.

It's sort of hard to read, but it looks like a 50 KVA, 13,200 volt primary. The secondary is 120/240. If this is so, the primary full-load current is 3.8 amps. The secondary current is 208 amps.

Climbing a pole like that is a bit uncomfortable until you get used to it. Your lower back, knees and ankles will be rather sore for a while. In this case, the top power line is the one with the voltage in it. The lower one (the one the orange hot-stick is hanging from) is grounded.

Rob

 

[InPhase277]

How strange... there appears to only be two guys watching the guy on the pole. Usually, there's at least four guys doing nothing.

 

[ScottR]

It's much easier to position the transformer if you have some line between the crane and the hook. Winching a transformer up a pole with no crane is quite a chore. That transformer likely weighs about 600 lbs.

The guy operating the crane was definitely new, or at least new to that equipment. A few times he extended the boom without playing out line and almost got the shackle caught in the top pulley (I'm not up on crane lingo, so hope you get the idea...)

I don't think they could have put the boom far enough above the high-volt line to clear the transformer.. Looked to me like the boom was too short. The crane operator got the old xformer out pretty smooth, but he dropped the new one a few inches onto the low voltage lines trying to squeeze it through.. I saw the guy on the pole wince a little, and it shook pretty good.

It's sort of hard to read, but it looks like a 50 KVA, 13,200 volt primary. The secondary is 120/240. If this is so, the primary full-load current is 3.8 amps. The secondary current is 208 amps.

Yup, it says CP3[cutoff] / 50+.. I just checked the full-size pics.

208A @ 240V?? That sounds small, considering many of my neighbors have 200A service and CAC. Though they were doing this work because our area would get frequent voltage drops (my lights dimmed when the neighbor's CAC compressor kicked on). They replaced all the low-volt wiring, and added a transformer down the line, splitting the block betw. that one and the one in the pics.

Thanks for all the info! :thumbsup:

How strange... there appears to only be two guys watching the guy on the pole. Usually, there's at least four guys doing nothing.

Heheheh, so true.

I give them credit though, the guy in the green vest actually came to my door yesterday (when they were replacing the lines) to tell me that they'd be doing work, and that my service would be disconnected. Nice guy too; put up with my questions. They cleaned up pretty good too.. The guy dropped some wiring scraps from the pole into my bushes -- they're gone now.

 

[jbfan]

How strange... there appears to only be two guys watching the guy on the pole. Usually, there's at least four guys doing nothing.

They don't work for GA power!:jester:

 

[spark plug]

208 Amps for a 50KVA Transformer doesn't jive (It don't Jive.) Sorry! It certainly does! At first glance it looks impossible! But when you take a calculator (or figure it in your head) you see that it checks out! Using the formula I = P over E. It's funny, I've installed many 200 Amp. Services (in Comm./Ind. applications) using a 75KVA transformer!!!

 

[InPhase277]

208 Amps for a 50KVA Transformer doesn't jive (It don't Jive.) Sorry! It certainly does! At first glance it looks impossible! But when you take a calculator (or figure it in your head) you see that it checks out! Using the formula I = P over E. It's funny, I've installed many 200 Amp. Services (in Comm./Ind. applications) using a 75KVA transformer!!!

A 3-phase 75 kVA transformer delivers the same amount of amps at 208 V as a single phase 50 kVA transformer: 208 A.

 

[jimmy21]

Wish they would come replace my xformer

 

[Magnettica]

We used climb utility poles like that during training in the Seabees. In school there'd be about 40 poles spread out about 6 feet apart from each other and we'd climb up there and throw volley balls around. If you dropped the ball or made a bad throw you'd have to "look, lock, drop" your way down to retrieve the ball, then climb back up. We did this for weeks at a time.

Micromind, I was under the impression that a 13.2 kv distribution line would be more likely found in an industrial neighborhood and something like 4160 is more commonly used in residential neighborhoods.


By the way, nice pictures for discussion.

 

[frenchelectrican]

We used climb utility poles like that during training in the Seabees. In school there'd be about 40 poles spread out about 6 feet apart from each other and we'd climb up there and throw volley balls around. If you dropped the ball or made a bad throw you'd have to "look, lock, drop" your way down to retrieve the ball, then climb back up. We did this for weeks at a time.

Micromind, I was under the impression that a 13.2 kv distribution line would be more likely found in an industrial neighborhood and something like 4160 is more commonly used in residential neighborhoods.


By the way, nice pictures for discussion.

Let me expand a little more related to the 13.2 KV now it is a common distribution line voltage the 4160 /2400 volt is typically found in older distribution area that slowly dropping out the only time we will see that voltage is primary feed to large commercal/ industrail user { especally true with very large service entrance set up and common to have a tranfomer inside the electrical room }

And the 13.2 is pretty much stanard voltage however there are few other voltage close to this number IIRC 12.2, 12.6, 14.8 KV's yeah some actally run much as 28KV as well all it depending on where the grid run.

Merci,Marc

 

[AndrewF]

I live in a somewhat rural area. The primary out here is 7200.

 

[TazinCR]

I don't understand. There are only 3 men. If the city was doing that there would be 7 workers, 3 engineers and they would still get it wrong.

 

[Speedy Petey]

You just gotta love pole and transformers in the middle of back yards. :laughing:

That jib crane truck is way cool though. I've never seen one like that before?

Was this by your house Scott?

 

[ScottR]

That jib crane truck is way cool though. I've never seen one like that before?

Agreed, very cool. Looks almost small enough that you could rent one at HD!

I'm pretty sure they use it exclusively for backyards and tight areas -- it fit nicely between the two houses when they were leaving, and went around shrubs/etc pretty good.

Was this by your house Scott?

Hah, yes. The service drop going to the bottom of the first pic is mine.. The guy on the pole could see into my bedroom if he turned around.. Good thing I thought to put pants on before taking the pics. :laughing:

 

[micromind]

You'd be amazed at what can be seen from the top of a pole, or in a bucket truck!

Not just houses either.

Rob

 

[coolfords]

A transformer in my backyard was replaced last night. The guys had a nifty little machine like the one in the pictures above.

The power had been out for several hours. It has been extremely hot down here (La Porte, TX) 100 plus everyday. I was glad to let them in my yard. lol

What are some common causes for a transformer to go bad? Is ( are ) the new one(s) better? Are they more efficient to me the consumer?

Just curious


Thanks

 

[WFO]

What are some common causes for a transformer to go bad? Is ( are ) the new one(s) better? Are they more efficient to me the consumer?

Just curious


Thanks

Recent standards have been passed that require all transformer manufacturers to meet extremely stringent efficiency guidelines. Of course, this also makes them much more expensive. They are generally rated in terms of full load losses (the energy dissipated as heat within the transformer itself at full load) and no load losses (the energy consumed with no load on the transformer).

Old ones in some ways were better than new ones in that they were larger (more oil = more cooling, more steel in the cores, etc.) which usually let them handle overloads better. When you design something with a slide rule
instead of a computer, you tend to build in a little more oomph.

Transformers will last decades if adequately protected from surges (lightning) and not overloaded for extended periods of time. The insulation is cellulose (paper) in oil (which also serves as an insulation and a heat transfer medium), which will degrade in time when exposed to heat, oxygen, or moisture. Eventually it can deteriorate to the point that it shorts internally.

 

[AllanJ]

I live in a somewhat rural area. The primary out here is 7200.

Given a sparser population, namely longer distances between homes, I would have expected the primary voltage to be higher.

Now a 12.5 KV (hot to hot aka phase to phase) 3 phase primary circuit has phase to ground voltage of approximately 7200 volts.

Also, if a system had pole transformers with 4160 volt primaries, designed for the older 2400/4160 volt feed, then it is conceivable that it could be upgraded to 4160 volt phase to ground and the equivalent phase to phase voltage is 7200. Raising the primary voltage allows the same wires to carry more watts with less percentage loss, and serve more or heavier users. There is still a limit to how high the voltage can go before other things like pole insulators need to be upgraded.

Most distribution circuits are three phase as they leave the substation although some streets will have just one or perhaps two of the phase conductors strung on the poles and supplying the houses. The nominal voltage is the phase to phase voltage, for example 12.5 KV phase to phase, 7200 volt phase to ground is called a 12.5 KV circuit. In order for a customer to have three phase power, all three phases of the distribution lines have to come down his street and usually three standard (single phase) pole transformers are installed side by side.

 

[spark plug]

issue of longevity of transformer life

The transofrmer windings (primary vs. secondary) are designed on a ratio basis. (usually 10/1)! The higher voltage range is reserved for long distance transmission. The medium range is usually for intra-city (sub-station) distribution. and the pole-transformers are actually called Distribution transformers. It's not practical (even if theoretically possible) to reduce voltage from 250,000 to 240v.!!!:yes::no::drinkon't Drink and Drive!!!

 

[micromind]

Generally speaking, the voltage of distribution lines (the ones that transformers that feed houses and such are connected to) are 2400/4160; 7200/12,470; 7616/13,200; 13,800 (usually a 3 wire delta, common in power plants), 13,200/22,860; 14,400/24,940; and 34,500 (again, usually a 3 wire delta, more transmission than distribution). This is not an exhaustive list, there are others but they're rare.

Transmission lines (the kind that go from power plants to substations or subs to subs) are usually 3 wire. The feed transformers are usually wye connected, and the neutral is used for ground fault detection only. The common voltages here are 34,500; 60,000; 69,000, 120,000; 230,000; 345,000, and 500,000. The highest voltage transmission line I've ever heard of is 765,000 volts. After you've worked on enough of these, you can pretty much tell what the voltage is just by looking at the line and insulators, though 60 and 69 look alot alike, and 345 and 500 look similar as well.

Sort of interesting to note, 34,500 connected delta is (obviously) 34,500. 34,500 connected wye is 60,000. 69,000 connected wye is 120,000.

Transformers are made that will reduce 500,000 volts to 120, but they're potential transformers. Very low current, usually milliamps. Used for instrumentation, not driving loads. These transformers are capacitor coupled, not core-and-coils. The ones I've seen are about 2' diameter and about 20' long, not counting the insulator on top.

All the different components that go into a transmission and distribution system are really interesting.
Well, to at least one of us anyway.

Rob